根据指定条件C＃从列表中选择随机数

Question

I'm trying to generate a unique random numbers from the list. Here user will input the followings:

1. Number of random numbers required
2. Number C1, C2 and C3 items.

Example: 10 Random numbers with C1-5, C2-4, and C3-1.

So based on these conditions a random number list need to generate.

My list looks like this

1   C1
2   C2
3   C3
4   C3
5   C2
6   C1
7   C2
8   C3
9   C1
10  C2
11  C1
12  C3
13  C3
14  C1
15  C2
16  C2
17  C4
18  C3
19  C4
20  C4
21  C4
22  C1
23  C2
24  C3
25  C4
26  C3
27  C4

My code looks like this:

protected void BtnGenerate_Click(object sender, EventArgs e)
{
            List<string> labels; // Holds all Labels (unique)
            List<string> values; // Holds all numbers of labels
            Random r = new Random();
            StringBuilder sb=new StringBuilder(100);

            sb.Clear();
            var randoms = values.OrderBy(x => r.Next()).Take(Convert.ToInt16(txtNumberOfRandomNumbers.Text));
            foreach (var item in randoms)
            {
                sb.Append(item.ToString() + ",");
            }

            lblRandomNumbers.Text = sb.ToString().Remove(sb.ToString().LastIndexOf(","));
}

I'm stuck with how to add these conditions to Random function. Please help me on this.

Answer 1

I suggest generating required items and then shuffling the colelction, eg:

// Simplest, but not thread safe
static Random s_Gen = new Random();

private static string Solution(int all, int c1, int c2, int c3) {
  return string.Join(",", new[] {
    Enumerable.Repeat("C1", c1),
    Enumerable.Repeat("C2", c2),
    Enumerable.Repeat("C3", c3),
    Enumerable.Repeat("C4", all - c1 - c2 - c3), }
  .SelectMany(item => item)
  .OrderBy(item => s_Gen.NextDouble()));  
}

protected void BtnGenerate_Click(object sender, EventArgs e) {
  lblRandomNumbers.Text = Solution(27, 10, 5, 3);
}

Answer 2

Try following :

List<string> input = new string[] { "C1", "C1", "C1", "C1", "C1", "C1", "C2", "C2", "C2", "C2", "C2", "C2", "C2", "C3", "C3", "C3", "C3", "C3", "C3", "C3", "C3", "C4", "C4", "C4", "C4", "C4", "C4" }.ToList();

Random rand = new Random();

List<string> output = input.Select(x => new { number = x, rand = rand.Next() }).OrderBy(x => x.rand).Select(x => x.number).ToList();